1. Field of the Invention
The present invention relates to industrial woven fabrics, especially for airbags, consisting of a filament yarn comprising coarse and fine thermoplastic filaments and having a yarn linear density between 30 and 1000 dtex, and to a process for producing the filament yarn.
2. Prior Art
Industrial woven fabrics, especially airbag woven fabrics, are produced using filament yarns composed of polyamides or polyesters and having a yarn linear density between about 50-750 denier (56-830 dtex), according to JP-A-01-104848. Such yarns can also consist of mixtures of different raw materials. Air permeability has been reduced in various ways. One way is to coat the woven fabrics with an elastomer. Such woven fabrics are generally stiff, heavy and complicated to produce. Owing to the high production costs, the reduced foldability and the limited recyclability, this solution has not been found to be very suitable. Another proposal is the production of uncoated woven fabrics in a closer weave and/or adapted finishing processes. With regard to foldability and weight, however, these wovens were not satisfactory. Air permeability can also be improved by calendering the woven fabrics, but this has the disadvantage of additional process steps and of impairment to the mechanical properties such as tenacity and tear strength in the warp and weft directions.
The production of a mixed linear density yarn having a yarn linear density of 50 to 800 dtex is also known from EP-A-0 022 065. The yarn, produced using a spinneret having different holes for coarse and fine filaments, is false twist textured and is said to exhibit a spunlike effect. It is intended for loose textile applications. It consists of a core filament group having a relatively coarse linear density and a sheath filament group having a relatively fine linear density, which surrounds the core group, and also not more than two further filaments having a filament linear density between 4.0 and 10 dtex. The spunlike yarn is not suitable for producing woven fabric possessing low air permeability and good tear strength.
Optimization in the direction of lower air permeability on the one hand and good foldability and low weight on the other have hitherto only been possible to a limited extent, since a high tensile strength and a (especially for airbags) high tear strength is not ensured. More particularly, lighter woven constructions exhibit a particularly high loss of tear strength.